1. Field of Invention
The present invention relates to an electro-optical apparatus and a method of driving an electro-optical material that allow display with less unevenness in luminance, a driving circuit therefor, an electronic apparatus, and a display apparatus.
2. Description of Related Art
Generally, in a passive-matrix liquid crystal apparatus, a plurality of scanning electrodes are formed on one substrate and a plurality of signal electrodes are formed on the other substrate, and liquid crystal is held between the substrates as an electrooptical material. Pixels are arranged respectively in association with intersections of the scanning electrodes and the signal electrodes so as to form a matrix. The intensity level of each pixel is determined according to a potential difference between associated scanning electrode and signal electrode.
MLS (Multi-Line Selection) driving, in which a plurality of scanning electrodes are simultaneously selected in a period and the selection period is divided into a plurality of sub-periods within a frame, can be used to drive the above apparatus. In MLS driving, a selection voltage is applied to a pixel a plurality of times in a frame, so that change is luminance of a pixel that is turned on for display is reduced compared with a method in which a selection voltage is applied only once in a frame, serving to avoid reduction in contrast. In the following description, the sub-periods into which one frame is divided will be referred to as fields.
A case where a liquid crystal panel having 4S scanning electrodes is driven by MLS driving is considered below. In this example, it is assumed that four scanning electrodes are simultaneously selected. In the following description, a set of scanning electrodes that are selected simultaneously will be referred to as a scanning electrode group. In this example, S scanning electrode groups G1, G2, . . . GS exist. Furthermore, the first scanning electrodes Y1, Y5, . . . Yk+1, . . . in the respective scanning electrode groups will be referred to as first scanning electrodes R1, the second scanning electrodes Y2, Y6, . . . Yk+2, . . . in the respective scanning electrode groups as second scanning electrodes R2, the third scanning electrodes Y3, Y7, . . . Yk+3, . . . in the respective scanning electrode groups as third scanning electrodes R3, and the fourth scanning electrodes Y4, Y8, . . . Yk+4, . . . in the respective scanning electrode groups as fourth scanning electrodes R4.
In MLS driving, either a positive voltage +V3 or a negative voltage xe2x88x92V3 with reference to a reference voltage VC is selected and applied to scanning electrodes. Each frame is divided into a first field f1, a second field f2, a third field f3, and a fourth field f4, and the scanning electrode groups are sequentially selected in each of the fields.
FIG. 18 is a chart showing polarities of scanning electrode voltage in MLS driving. In FIG. 18, xe2x80x9c+1xe2x80x9d indicates selection of +V3 as a scanning electrode voltage, whereas xe2x80x9cxe2x88x921xe2x80x9d indicates selection of xe2x88x92V3 as a scanning electrode voltage. Furthermore, sets of polarities of selection voltages to be applied respectively to the first to fourth scanning electrodes R1 to R4 that are selected simultaneously will be referred to as first to fourth scanning patterns P1 to P4, and sets of scanning patterns will be referred to as scanning pattern sets. In the example shown in FIG. 18, a column corresponds to a scanning pattern, and a set of the first column to the fourth column corresponds to a scanning pattern set. For example, if the first to fourth scanning patterns P1 to P4 are sequentially used in the first to fourth fields f1 to f4, voltage applied to the first scanning electrodes R1 is +V3 in the first field f1, +V3 in the second field f2, xe2x88x92V3 in the third field f3, and +V3 in the fourth field f4.
Signal electrode voltages are selected from +V2, xe2x88x92V2, +V1, xe2x88x92V1, and VC. A relationship among the potentials +V3, xe2x88x92xe2x88x92V3, +V2, xe2x88x92V2, +V1, xe2x88x92V1, and VC is shown in FIG. 19. Signal electrode voltages are selected based on the number of mismatches between a scanning pattern and a pattern of display data D (hereinafter referred to as a display pattern). If display data D to be displayed on a pixel is off (black) for xe2x80x9c0xe2x80x9d and on (white) for xe2x80x9c1,xe2x80x9d xe2x80x9c0xe2x80x9d is associated with xe2x80x9cxe2x88x921xe2x80x9d and xe2x80x9c1xe2x80x9d is associated with xe2x80x9c+1.xe2x80x9d
FIG. 20 is a chart showing an example of selection of signal electrode voltages. In this example, +V2 is selected as a signal electrode voltage if the number of mismatches between scanning pattern and display pattern is xe2x80x9c4,xe2x80x9d +V1 is selected as a signal electrode voltage if the number of mismatches is xe2x80x9c3,xe2x80x9d VC is selected as a signal electrode voltage if the number of mismatches is xe2x80x9c2,xe2x80x9d xe2x88x92V1 is selected as a signal electrode voltage if the number of mismatches is xe2x80x9c1,xe2x80x9d and xe2x88x92V2 is selected as a signal electrode voltage if the number of mismatches is xe2x80x9c0.xe2x80x9d
It can be assumed, as an example, that display pattern corresponding to the first to fourth scanning electrodes R1 to R4 is xe2x80x9cxe2x88x921, xe2x88x921, xe2x88x921, xe2x88x921.xe2x80x9d Since the first scanning pattern P1 is xe2x80x9c+1, xe2x88x921, +1, +1,xe2x80x9d the number of mismatches is xe2x80x9c3.xe2x80x9d Accordingly, if display pattern is xe2x80x9cxe2x88x921, xe2x88x921, xe2x88x921, xe2x88x921xe2x80x9d as shown in FIG. 20, +V1 is selected as a signal electrode voltage.
If a combination of polarities of scanning electrode voltages simultaneously selected are such that only one of four is mismatched as described above, for example, when all pixels on a signal electrode are off, the signal electrode voltage forms a waveform Q1 shown in FIG. 21, whereby +V1 is applied uniformly throughout one frame. On the other hand, if all pixels on a signal electrode are on, the signal electrode voltage forms a voltage waveform Q2 shown in FIG. 21, whereby xe2x88x92V1 is applied uniformly throughout one frame.
Accordingly, variation in voltages applied to pixels in a non-selection period is eliminated. That is, if a combination of polarities of scanning electrode voltages simultaneously selected is such that only one of four is mismatched, variation in signal electrode voltages is reduced when displaying black text in white background, which is most typical, or when displaying white text in black background.
In MLS driving, however, signal electrode voltages are selected according to a combination of scanning pattern and display pattern. Thus, signal electrode voltages are fixed to a specific pattern in relation to a specific display pattern. FIG. 22 shows an example of display pattern. In this example, black is displayed at pixels indicated by oblique lines while white is displayed at the other pixels, the display pattern shown in FIG. 22 being repeated in the rightward direction and in the downward direction. Signal electrode voltages are selected according to a table shown in FIG. 20.
In this case, the first to fourth columns from the left always display xe2x80x9cwhite.xe2x80x9d Thus, display pattern of these columns is always xe2x80x9c+1, +1, +1, +1,xe2x80x9d so that voltages at the signal electrodes X1 to X4 are always xe2x88x92V1. On the other hand, the fifth to eighths columns from the left repeatedly displays xe2x80x9cwhite, white, white, black, and black, black, black, white.xe2x80x9d Thus, display pattern of G1 and G3 in these columns is always xe2x80x9c+1, +1, +1, xe2x88x921,xe2x80x9d so that voltages at the signal electrodes X5 to X8 are always VC or xe2x88x92V2.
Display pattern of G2 and G4 in these columns is always xe2x80x9cxe2x88x921, xe2x88x921, xe2x88x921, +1,xe2x80x9d so that voltages at the signal electrodes X5 to X8 are always VC or +V2. That is, voltages at the signal electrodes X1 to X4 are always xe2x88x92VC, whereas voltages at the signal electrodes X5 to X8 are always VC or xc2x1V2.
Since the signal electrodes oppose the scanning electrodes via liquid crystal, capacitance is present. Furthermore, capacitance of liquid crystal changes depending on a voltage being applied.
Thus, actual voltage waveforms at the signal electrodes do not rise or fall sharply, and include distortions attributable to capacitive component.
The degree of distortion of the voltage waveforms is determined according to frequency components of the voltage waveforms. In the example described above, voltages at the signal electrodes X1 to X4 are always xe2x88x92VC, so that distortion is substantially absent. In contrast, voltages at the signal electrodes X5 to X8 are VC or +V2, so that distortion of waveforms is larger compared with the voltages at the signal electrodes X1 to X4. Luminance of each pixel is determined according to the effective voltage applied to liquid crystal. Thus, pixels driven by signal electrode voltages with less distortion and pixels driven by signal electrode voltages with larger distortion differ in luminance. In this example, white displayed on the first to fourth columns and white displayed on the fifth to eighth columns differ in luminance. Accordingly, unevenness in luminance occurs every four columns.
As described above, in MLS driving, signal electrode voltages are fixed to a specific pattern in relation to a specific display pattern, causing unevenness in luminance. A technique to address or solve this problem is disclosed in Japanese Unexamined Patent Application Publication No. 7-281645. According to the technique, a plurality of scanning patterns are sequentially selected, so that bias will not be present in frequency components of voltage waveforms at signal electrodes. As described above, which voltage to select for application to signal electrodes is determined based on a display pattern and a scanning pattern. Thus, even if the display pattern is fixed, bias in frequency components of voltage waveforms at signal electrodes can be removed by changing the scanning pattern.
Signal electrode voltages must be selected based on a display pattern and a scanning pattern. Thus, when the arrangement is such that a plurality of scanning patterns are alternately used, a processing circuit becomes complex.
A type of such a processing circuit includes a plurality of switches respectively associated with signal electrodes, and a memory. Each of the switches selects and outputs a voltage from a plurality of voltages based on selection data. The memory stores in advance a display pattern and a scanning pattern set in association with selection data. In such an arrangement, required capacity of the memory doubles when the number of scanning pattern doubles.
The present invention addresses the above situation, and provides a method of driving an electro-optical apparatus in which a plurality of scanning pattern sets can be alternated in a simple construction, a driving circuit, and an electronic apparatus.
In order to address or solve the problems described above, a method of driving an electro-optical apparatus according to the present invention is used in an electrooptical apparatus constructed such that a plurality of scanning electrodes and a plurality of signal electrodes are disposed so as to hold an electro-optical material therebetween and to cross each other, the plurality of scanning electrodes are divided into a plurality of scanning electrode groups that each have a predetermined number of scanning electrodes, a scanning electrode group is selected a plurality of times in each frame, a positive selection voltage or a negative selection voltage with reference to a reference voltage at a center potential is applied to each of the scanning electrodes belonging to the scanning electrode group during the selection period according to a scanning pattern set including a plurality of predetermined scanning patterns, a display pattern that specifies whether to turn on or turn off a plurality of pixels associated with intersections on the scanning electrodes belonging to the scanning electrode group is compared with the scanning pattern, and voltages selected from a plurality of predetermined voltages are applied respectively to the signal electrodes based on the number of mismatches between elements of the display pattern and elements of the scanning pattern. A first and a second scanning pattern sets are alternately used on a basis of a predetermined period to apply voltages respectively to the scanning electrodes and to apply voltages respectively to the signal electrodes, and the first scanning pattern set is such that elements associated with a scanning electrode are inverted in the second scanning pattern set.
According to this invention, the signal electrodes are driven using the two scanning pattern sets, so that bias in frequency components of signal electrode voltages is removed. Furthermore, since the first scanning pattern set is such that elements associated with a scanning electrode are inverted in the second scanning pattern set. Thus, when scanning electrodes are driven according to the first scanning pattern set, voltages to be applied respectively to signal electrodes can be determined based on the number of mismatches between a display pattern in which elements associated with the scanning electrode are inverted and scanning patterns belonging to the second scanning pattern set.
Preferably, the first scanning pattern set is applied to some of the scanning electrode groups, whereas the second scanning pattern set is applied to the other scanning electrode groups. More preferably, adjacent scanning electrode groups are driven using different scanning pattern sets. According to this invention, scanning pattern sets are alternated within one frame, so that bias in frequency components of signal electrode voltage is further removed.
Furthermore, preferably, the electro-optical material is liquid crystal, voltages of a polarity indicated by the scanning pattern and voltages of a polarity opposite to the polarity indicated by the scanning pattern are alternately applied to the scanning electrodes on a basis of a predetermined period of inversion, and the first scanning pattern set and the second scanning pattern set are alternated on a basis of each period of the inversion of polarity. In particular, if the period of inversion is two frames, preferably, in a two-frame period, the first scanning pattern set is applied to a first scanning electrode group of a pair of adjacent scanning electrode groups whereas the second scanning pattern set is applied to a second scanning electrode group thereof, and in a next two-frame period, the second scanning pattern set is applied to the first scanning electrode group of the pair of adjacent scanning electrode groups whereas the first scanning pattern set is applied to the second scanning electrode group.
When liquid crystal, which is an electro-optical material, is driven by AC, polarities of voltages applied to the scanning electrodes are inverted on a basis of a predetermined inversion period. If driving ability of a circuit that applies voltages to the signal electrodes is low, distortion in voltage waveforms at the signal electrodes varies depending on the scanning pattern sets. Thus, if the scanning pattern sets are alternated within one inversion period, DC voltage may be applied to the liquid crystal. Accordingly, in the invention described above, the association between the scanning electrode groups and the scanning pattern sets is fixed within an inversion period, while the association between the scanning electrode groups and the scanning pattern sets is alternated on a basis of each inversion period.
Also preferably, the relationship of each of the scanning patterns belonging to the second scanning pattern set and the display pattern to voltages to be applied to the signal electrodes is stored in advance, when the first scanning pattern set is applied, display data associated with scanning electrodes associated with inverted elements in the second scanning pattern set is inverted, the display pattern is generated based on the inverted display data, and voltages to be applied to the signal electrodes are determined based on the generated display pattern and the scanning patterns and with reference to stored content.
Voltages to be applied to the signal electrodes are determined based on the number of mismatches obtained by comparing elements of the scanning patterns and elements of the display pattern. The display pattern is determined based on display data. Thus, if an alternative scanning pattern with different elements is used instead of a scanning pattern, display data associated with mismatched elements are inverted, and voltages to be applied to the signal electrodes are determined based on the number of mismatches between the display pattern thus generated and the scanning pattern. The invention described above has been made in view of the above, and according to the invention, the relationship between the second scanning pattern set and voltages to be applied to the signal electrodes is stored in advance, and voltages to be applied to the signal electrodes are determined based on a display pattern generated by inverting particular display data when the first scanning pattern set is applied.
Accordingly, the relationship between the first scanning pattern set and voltages to be applied to the signal electrodes need not be stored in advance.
A driving circuit to drive an electro-optical apparatus according to the present invention is used in an electro-optical apparatus constructed such that a plurality of scanning electrodes and a plurality of signal electrodes are disposed so as to hold an electrooptical material therebetween and to cross each other. The driving circuit is provided such that the plurality of scanning electrodes are divided into a plurality of scanning electrode groups that each have a predetermined number of scanning electrodes; a scanning electrode group is selected a plurality of times in each frame; a positive selection voltage or a negative selection voltage with reference to a reference voltage at a center potential is applied to each of the scanning electrodes belonging to the scanning electrode group during the selection period according to a scanning pattern set including a plurality of predetermined scanning patterns; a display pattern that specifies whether to turn on or turn off a plurality of pixels associated with intersections on the scanning electrodes belonging to the scanning electrode group is compared with the scanning pattern; and voltages selected from a plurality of predetermined voltages are applied respectively to the signal electrodes based on the number of mismatches between elements of the display pattern and elements of the scanning pattern. The driving circuit includes a storage device that stores scanning patterns constituting a reference scanning pattern set that is one of a plurality of scanning pattern sets, and a display pattern, in association with selection data for selecting voltages to be applied to the signal electrodes; a scanning pattern control device that generates a scanning pattern control signal for selecting one of the scanning patterns according to a predetermined rule; a data control device that determines which scanning pattern set to use and for inverting display data based on mismatch between elements in the scanning pattern set determined and elements in the reference scanning pattern set; a display pattern generating device that generates a display pattern based on output data from the data control unit; and a signal electrode voltage application device that applies voltages to signal electrodes according to selection data read from the storage device based on the display pattern generated by the display pattern generating device and the scanning pattern control signal.
According to this invention, the data control device determines which scanning pattern set to use, and inverts display data based on mismatch between elements in s scanning pattern set determined and the reference scanning pattern set. Thus, it suffices for the storage device to store only selection data corresponding to the reference scanning pattern set. Accordingly, required storage capacity of the storage device can be considerably reduced.
The driving circuit according to the present invention may further include a scanning electrode voltage application device to apply voltages to the scanning electrodes based on the scanning pattern control signal.
Furthermore, preferably, the number of the plurality of scanning pattern sets is two, the scanning pattern set other than the reference scanning pattern set is such that elements associated with a scanning electrode are inverted in the reference scanning pattern set, and the data control device inverts display data associated with the scanning electrode for output when the scanning pattern set other than the reference scanning pattern set is used. In that case, display data associated with a particular horizontal scanning line is to be inverted. Thus, for example, the data control device counts a horizontal synchronization signal and inverts display data based on the count, which can be implemented in a simple construction.
An electronic apparatus according to the present invention includes an electro-optical panel constructed such that a plurality of scanning electrodes and a plurality of signal electrodes are disposed so as to hold an electro-optical material therebetween and to cross each other; and a driving circuit to drive the electro-optical panel, in which the plurality of scanning electrodes are divided into a plurality of scanning electrode groups that each have a predetermined number of scanning electrodes, a scanning electrode group is selected a plurality of times in each frame, a positive selection voltage or a negative selection voltage with reference to a reference voltage at a center potential is applied to each of the scanning electrodes belonging to the scanning electrode group during the selection period according to a scanning pattern set including a plurality of predetermined scanning patterns, a display pattern that specifies whether to turn on or turn off a plurality of pixels associated with intersections on the scanning electrodes belonging to the scanning electrode group is compared with the scanning pattern, and voltages selected from a plurality of predetermined voltages are applied respectively to the signal electrodes based on the number of mismatches between elements of the display pattern and elements of the scanning pattern. The driving circuit includes a storage device that stores scanning patterns constituting a reference scanning pattern set that is one of a plurality of scanning pattern sets, and a display pattern, in association with selection data for selecting voltages to be applied to the signal electrodes; a scanning pattern control device that generates a scanning pattern control signal for selecting one of the scanning patterns according to a predetermined rule; a data control device that determines which scanning pattern set to use and that inverts display data based on mismatch between elements in the scanning pattern set determined and elements in the reference scanning pattern set; a display pattern generating device that generates a display pattern based on output data from the data control unit; and a signal electrode voltage application device that applies voltages to signal electrodes according to selection data read from the storage device based on the display pattern generated by the display pattern generating device and the scanning pattern control signal. Such electronic apparatuses include, for example, various display apparatuses, such as television sets and monitors, communication apparatuses, such as cellular phones and PDAs, and information processing apparatuses, such as personal computers, for example.
In a method of driving an electro-optical material according to the present invention, four of a plurality of scanning electrodes to select a plurality of electro-optical materials are simultaneously selected and a signal voltage defining intensity levels of display by the plurality of electro-optical materials are applied to signal electrodes in each of four fields within one frame. The method of driving an electro-optical material includes a first step of applying either a first voltage or a second voltage of the same magnitude and a different polarity with respect to the first voltage to the signal electrodes as the signal voltage; and a second step of applying one of a third voltage of a different magnitude with respect to the first and second voltages, a fourth voltage of the same magnitude and a different polarity with respect to the third voltage, and a center voltage between the third and fourth voltages, to the signal electrodes as the signal voltage. Preferably, the first step and the second step are alternately executed on a basis of each field.
According to these features, voltages respectively applied as the signal voltage in the first step and in the second step are certain to differ from each other. Accordingly, bias in frequency components of signal voltages is removed.
In a driving circuit to drive an electro-optical material according to the present invention, four of a plurality of scanning electrodes for selecting a plurality of electro-optical materials are simultaneously selected and a signal voltage defining intensity levels of display by the plurality of electro-optical materials are applied to signal electrodes in each of four fields within one frame. Either a first voltage or a second voltage of the same magnitude and a different polarity with respect to the first voltage is applied to the signal electrodes as the signal voltage; and one of a third voltage of a different magnitude with respect to the first and second voltages, a fourth voltage of the same magnitude and a different polarity with respect to the third voltage, and a center voltage between the third and fourth voltages, is applied to the signal electrodes as the signal voltage. Preferably, application of either the first voltage or the second voltage and application of one of the third voltage, the fourth voltage, and the center voltage are alternately executed on a basis of each field.
A display apparatus according to the present invention includes the driving circuit to drive an electro-optical material as described above.